Clock fails to start (edited for clarity)

[bob jenkins]

I agree with the other answers related to preventing the problem.

If the official noticed that the clock didn't start, stop play, run off the time (assuming there was a count) and resume.

It's not "allowed" but the "fairest" answer might be the "do-over" -- if it's noticed early enough.

Or, the official can yell (so others hear it), "Clock -- I've got a count" -- and count the four seconds.

If none of that happened, then, if the officials had a count, use it. IF the officials didn't have a count, then they have to go by the clock / horn.